For example, electro-magnetic interference (EMI) noise generated by the high speed switching operation of an inverter of a power conversion device that controls an alternating current (AC) driving motor serving as a load device becomes conduction noise and flows in a power source line and the earth; and accordingly, the noise is transmitted to other electrical apparatus to have the possibility of harmful influence such as causing an erroneous operation. There were two types of noise: normal mode noise that is transmitted in a transmission path between a power source and the load device; and common mode noise that is transmitted between the transmission path and the earth. A noise filter is used as a countermeasure that reduces these types of noise and, more particularly, there is a dual mode choke coil serving as the noise filter that reduces both types of noise.
For example, a noise filter in Patent Document 1 discloses that, in first and second common mode choke coils which are for suppressing common mode noise that forms EMI noise from being transmitted to the power source side, the first common mode choke coil forms a first magnetic substance core having a pair of magnetic legs formed with a protrusion part on both ends of the first magnetic substance core; the second common mode choke coil forms a second magnetic substance core which has the same configuration as the first magnetic substance core, and whose protrusion parts on both ends of the second magnetic substance core are disposed so as to be opposite to the protrusion parts on both ends of the first magnetic substance core via air gaps. Further, the winding directions of windings of the same phase, which are wound around the respective magnetic legs opposite to each other via the air gap between the first and second magnetic substance cores are reversed, and a high impedance against normal mode noise is obtained by magnetic flux of a magnetic circuit formed by the windings of the same phase; and this removes normal mode choke coils to achieve a reduction in size of the filter.